The rectal finger exam, is only any use, if the Tumours are on that side of the Prostate - I had about 4 or 5 fingers - "Nothing wrong" they said, before a PSA test of 27, made them look deeper - I suspect, he probably has tumours on the opposite side like mine.
The MRI should give them an idea, it will probably be followed by Biopsies. Mine was.
It does sound like a "slow-grower" like mine.
Mine was sorted out with Hormone & Radio therapy. I'm still here 5 years later ! So I guess it worked. HT & RT takes time, but it's not invasive.
Wish Dad All the best & not to worry. There are some wonderful treatments available.